Magnetic sensor, production process of the magnetic sensor and magnetic array suitable for the production process

ABSTRACT

The present invention aims to provide a magnetic sensor provided with a magnetoresistive effect element capable of stably maintaining a direction of magnetization in a magnetic domain of a free layer.  
     The magnetic sensor includes a mangetoresistive effect element provided with narrow zonal portions  11   a . . .    11   a  including a pinned layer and a free layer. Disposed below both ends of the free layer are bias magnet films  11   b . . .    11   b  composed of a permanent magnet that applies to the free layer a bias magnetic field in a predetermined direction and an initializing coil  31  that is disposed in the vicinity of the free layer and applies to the free layer a magnetic field having the direction same as that of the bias magnetic field by being energized under a predetermined condition. Further, magnetizing the bias magnet films and fixing the direction of magnetization of the pinned layer are performed by a magnetic field formed by a magnet array configured such that plural permanent magnets are arranged on a lattice point of a tetragonal lattice and a polarity of a magnet pole of each permanent magnet is different from a polarity of the other adjacent magnet pole spaced by the shortest route.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a magnetic sensor using amagnetoresistive effect element including a pinned layer and a freelayer, a production process of the magnetic sensor and a magnet arraysuitable for the production process.

[0003] 2. Description of the Related Arts

[0004] Conventionally, a magnetoresistive effect element is applied to amagnetic sensor. For instance, the magnetoresistive effect elementincludes a giant magnetoresistive effect element (GMR element) or thelike that is provided with a pinned layer having magnetization pinned(fixed) in a predetermined direction and a free layer in which thedirection of magnetization is changed according to an external magneticfield and that presents a resistance value according to a relativerelationship between the direction of magnetization in the pinned layerand the direction of magnetization in the free layer. In the magneticsensor of this type, it is required that the direction of magnetizationin each magnetic domain in the free layer in case where the externalmagnetic field is not applied to the magnetic sensor is stablymaintained in a predetermined direction (this predetermined direction isreferred to as “Initial-state direction hereinafter) in order toaccurately detect a minute external magnetic field.

[0005] In general, a thin free layer is shaped into a rectangle asviewed in a plane and the long side (long axis) of the rectangular ismatched to the initial-state direction, whereby the direction in eachdomain in the free layer is matched to the initial-state direction byutilizing a shape anisotropy in which the direction of magnetization isaligned in the longitudinal direction. Further, a bias magnet film thatis a permanent magnet film is disposed at both end sections of thelongitudinal direction of the free layer to apply the magnetization inthe initial-state direction to the free layer so that the direction ofmagnetization in each magnetic domain in the free layer is returned tothe initial-state direction, with a long-term stability, whenever theexternal magnetic field disappears (see. Japanese Laid open publication2002-299728 (FIGS. 42-44)).

[0006] The state of magnetization in the free layer and the bias magnetfilm as described above will be explained with reference to FIG. 17 thatis a plan view of the free layer and the bias magnet film. In FIG. 17, afree layer 100 is formed to have a longitudinal direction in an X-axisdirection, and a pair of bias magnet films 101 and 102 are arranged atboth ends of the longitudinal direction.

[0007] At a stage of forming these films, the directions ofmagnetization in each magnetic domain of the free layer 100 and the biasmagnet films 101 and 102 are not aligned to the initial-state directionthat is the longitudinal direction of the free layer as shown by arrowsin FIG. 17A. When an external magnetic field whose magnitude is changedin a direction (Y-axis direction) perpendicular to the longitudinaldirection of the free layer is applied to the magnetic sensor in whichthe free layer 100 and the bias magnet films 101 and 102 are inabove-mentioned state, for measuring a resistance value of the magneticsensor, a hysteresis occurs as shown in FIG. 18A. As apparent from this,in the magnetic sensor wherein the directions of magnetization in thefree layer 100 and the bias magnet films 101 and 102 are not aligned tothe longitudinal direction of the free layer, the resistance value forthe external magnetic field being in the vicinity of “0” fluctuates in arange shown by an arrow in FIG. 18A, resulting in that the magneticsensor cannot accurately detect a minute magnetic field.

[0008] Subsequently, when a magnetic field having a magnitude greaterthan a coersive force Hc of the bias magnet films 101 and 102 is appliedin the longitudinal direction (X-axis positive direction) to themagnetic sensor in which the free layer 100 and the bias magnet films101 and 102 are in a state shown in FIG. 17A in order to perform aninitialization of the free layer 100 and the magnetization of the biasmagnet films 101 and 102, the directions of magnetization in eachmagnetic domain in the free layer 100 and the bias magnet films 101 and102 are matched to the initial-state direction as shown in FIG. 17B.

[0009] When an external magnetic field whose magnitude is changed withina range smaller than the coersive force Hc of the bias magnet films 101and 102 in the Y-axis direction is applied to the magnetic sensor whichis in the above-mentioned state, the direction of magnetization in themagnetic domain in the free layer 100 is changed as shown in FIG. 17C,and then, after eliminating the external magnetic field, the directionof magnetization in each magnetic domain in the free layer 100 isreturned to the initial-state direction as shown in FIG. 17D like thatas shown in FIG. 17B. When the resistance value of the magnetic sensoris measured in this case, the hysteresis is decreased, so that theresistance value for the external magnetic field being in the vicinityof “0” becomes approximately constant. Accordingly, the magnetic sensorhaving the free layer 100 initialized and the bias magnet films 101 and102 magnetized can accurately detect a minute magnetic field.

[0010] However, when an external magnetic field having a magnitudesmaller than the coersive force of the magnet films 101 and 102 butrelatively great and having a main component in the direction (X-axisnegative direction) reverse to the initial-state direction is applied tothe magnetic sensor (the magnetic sensor having the free layer 100initialized and the bias magnet films 101 and 102 magnetized), thedirection of magnetization in each magnetic domain in the free layer ischanged from the state shown in FIG. 19A to the state shown in FIG. 19B,and even if the external magnetic field is eliminated, the direction ofmagnetization in each magnetic domain in the free layer 100 does notmatch (return) to the initial-state direction. As a result, the magneticsensor has a hysteresis again with respect to the external magneticfield, entailing a problem of deteriorating the detection accuracy ofthe magnetic field.

SUMMARY OF THE INVENTION

[0011] Accordingly, one of objects of the present invention is toprovide a magnetic sensor capable of satisfactorily maintaining adetection accuracy even after a great external magnetic field is appliedthereto. Further, another object of the present invention is to providea magnetic sensor capable of efficiently magnetizing the aforesaid biasmagnet films, a production process of the magnetic sensor and a magnetarray suitable for the production process.

[0012] According to the feature of the present invention, a magneticsensor comprising a magnetoresistive effect element including a pinnedlayer and a free layer comprises a bias magnet film composed of apermanent magnet for producing a bias magnet field for (in) the freelayer in a predetermined direction and an initializing coil that isprovided in the vicinity of the free layer and applies to the free layera magnetic field in the direction same as the direction of the biasmagnetic field by being energized under a predetermined condition.

[0013] According to the above structure, the initializing coil isenergized under a predetermined condition to thereby generate aninitializing magnetic field for returning the direction of magnetizationin each magnetic domain in the free layer to the direction same as thedirection of the bias magnetic field by the bias magnet film, wherebythe direction of magnetization in each magnetic domain in the free layercan be corrected even if the direction of magnetization is disturbed dueto some reason such as when a strong magnetic field is applied to themagnetic sensor. As a result, a change in the resistance value to themagnetic field does not have hysteresis, whereby a magnetic sensor canbe provided that can detect even a minute magnetic field with highprecision over a long period.

[0014] Another feature of the present invention is that a productionprocess of a magnetic sensor comprising, on a substrate, a pinned layer,a free layer and a bias magnet film being a permanent magnet thatapplies a bias magnetic field to the free layer to form amagnetoresistive effect element having a resistance value varyingaccording to a relative angle made by a direction of magnetization inthe pinned layer and a direction of magnetization in the free layer,comprises a step of preparing a magnet array configured such that pluralpermanent magnets are arranged on a lattice point of a tetragonallattice and a polarity of a magnet pole of each permanent magnet isdifferent from a polarity of the other adjacent magnet pole spaced bythe shortest route (i.e., shortest distance), a step of manufacturing awafer, including the substrate(s), on which plural island-like elementfilms are interspersed, each element film including a film that becomesthe pinned layer, a film that becomes the free layer and a film thatbecomes the bias magnet film and a step of disposing (placing,arranging) the wafer in the vicinity of the magnet array so as toestablish a predetermined relative positional relationship between thewafer and the magnet array and magnetizing the film that becomes thebias magnet film of the plural element films by utilizing a magneticfield formed between one magnet pole of the magnet poles of the magnetarray and other magnet pole, of the magnet poles of the magnet array,that is adjacent to the one magnet pole spaced by the shortest route(from the one magnet pole).

[0015] The magnet array is configured such that plural permanent magnetsare arranged at a lattice point of a tetragonal lattice and the polarityof the magnetic pole of each permanent magnet is different from thepolarity of the other adjacent magnetic pole spaced by the shortestroute (in the same plane), as viewed in a plane. Accordingly, thefollowing magnetic fields are formed above the magnet array as viewed ina plane of the magnet array: a magnetic filed formed from one N-pole inthe rightward direction to S-pole that is present at the right side ofthe N-pole, a magnetic field formed from the N-pole in the upwarddirection to S-pole that is present at the upper side of the N-pole, amagnetic field formed from the N-pole in the leftward direction toS-pole that is present at the left side of the N-pole and a magneticfield formed from the N-pole in the downward direction to S-pole that ispresent at the lower side of the N-pole (see FIG. 13). Similarly, thefollowing magnetic fields are formed to (toward) some S-pole: a magneticfield formed in the leftward direction from N-pole that is present atthe right side of this S-pole, a magnetic field formed in the downwarddirection from N-pole that is present at the upper side of this S-pole,a magnetic field formed in the rightward direction from N-pole that ispresent at the left side of this S-pole and a magnetic field formed inthe upward direction from N-pole that is present at the lower side ofthis S-pole.

[0016] In this process, a wafer, including the substrate(s), on whichplural island-like element films is interspersed, each element filmincluding a film that becomes the pinned layer, a film that becomes thefree layer and a film that becomes the bias magnet film is disposed(placed, set, or arranged) in the vicinity of the magnet array so as toestablish a predetermined relative positional relationship between thewafer and the magnet array and thereby the film that becomes the biasmagnet film of the plural element films is magnetized by utilizing theabove-mentioned magnetic field formed by the magnet array. Therefore, amagnetic sensor wherein magnetization directions of the bias magnetfilms are crossed (perpendicular in this case) to each other on a singlesubstrate (a monolithic substrate) can efficiently be manufactured.

[0017] More specifically, the step of manufacturing the wafer includes astep of forming each film, that becomes the free layer, of the pluralelement films in such a manner as to have a shape with a long axis and ashort axis, and in such a manner that at least one of the long axes ofthe films, that become the free layers, of the plural element films isperpendicular to the long axis of the other film, that becomes the freelayer, of the plural element films, and a step of forming the film thatbecomes the bias magnet film at both ends of each film, that becomes thefree layer, in the direction of the long axis, wherein the predeterminedrelative positional relationship in the step of magnetizing the filmthat becomes the bias magnet film is a relative relationship, betweenthe wafer and the magnet array, that matches the direction ofmagnetization of the film that becomes the bias magnet film with thedirection of the long axis of the film that becomes the free layerhaving the bias magnet film provided at both ends thereof, by a magneticfield formed by the magnet array.

[0018] Further, in this case, it is preferable to include a step ofarranging the wafer in the vicinity of the magnet array so as toestablish a relative positional relationship, between the wafer and themagnet array, that is different from the predetermined relativepositional relationship, whereby the direction of magnetization of thefilm, that becomes the pinned layer, of the plural element films ispinned by utilizing the magnetic field formed by the magnet array.

[0019] According to this method, the magnet array used for magnetizingthe film that becomes the bias magnet film is also used for fixing thedirection of magnetization in the pinned layer, whereby a magneticsensor (two-axis magnetic sensor that can detect the respective magneticfields whose directions are perpendicular to each other) whereinmagnetization directions of the bias magnet films are crossed(perpendicular in this case) to each other on a single substrate canefficiently be manufactured with low cost.

[0020] Moreover, the present invention provides a magnet arrayconfigured such that plural permanent magnets, each having anapproximately rectangular parallelepiped shape in which the sectionalshape perpendicular to one central axis of the rectangularparallelepiped is approximately square, are arranged such that thecenter of gravity of the edge face having approximately square shape ismatched with a lattice point of the tetragonal lattice, and the polarityof the magnetic pole of each permanent magnet thus arranged is differentfrom the polarity of the magnetic pole of the adjacent other permanentmagnet spaced by the shortest route.

[0021] That is, this magnet array is the one where the plural permanentmagnets are disposed such that the center of gravity of the edge facehaving approximately square shape is matched with a lattice point of thetetragonal lattice, a side of the edge face having said approximatelysquare shape is on the same line on which a side of the other edge facedisposed in the same row, the edge faces are in a single same plane, andthe polarity of the magnetic pole of each permanent magnet thus arrangedis different from the polarity of the magnetic pole of the adjacentother permanent magnet spaced by the shortest route.

[0022] As described above, magnetizing each film that becomes the biasmagnet film and/or fixing the direction of magnetization in the layerthat becomes the pinned layer of the above-mentioned two-axis magneticsensor can efficiently be performed by using the magnet array, forexample. Therefore, with the magnet array, it is possible to manufacturethe two-axis magnetic sensor with low cost.

[0023] Further, this magnet array can be “A magnet array includingplural permanent magnets, each having an approximately rectangularparallelepiped shape and having a sectional shape, perpendicular to onecentral axis of the rectangular parallelepiped, which is approximatelysquare, and each having poles formed at both edge faces, one of whichhas the approximately square shape perpendicular to the central axis ofthe rectangular parallelepiped; wherein

[0024] the plural permanent magnets are arranged in such a manner thateach center of gravity of the edge faces having the approximately squareshape is matched with a lattice point of a tetragonal lattice, a certainside of sides forming one of the edge faces of the plural permanentmagnets disposed in a certain row of the tetragonal lattice and acertain side of sides forming one of the edge faces of the other pluralpermanent magnets disposed in the same row of the tetragonal lattice isin a same straight line, all the edge faces having the square shapes ofthe permanent magnets are placed in an approximately same single plane,and any two of the polarities of the magnetic poles of the permanentmagnets disposed adjacent each other and spaced by the shortest routeare different each other.” and this array can preferably be used tomagnetize the bias magnetic films and the like of the magnetic sensormentioned above.

[0025] In addition, “A magnet array including plural permanent magnets,each having an approximately rectangular parallelepiped shape and havinga sectional shape, perpendicular to one central axis of the rectangularparallelepiped, which is approximately square, and each having polesformed at both edge faces, one of which has the approximately squareshape perpendicular to the central axis of the rectangularparallelepiped and a thin plate-like yoke formed of a magnetic material;wherein

[0026] the plural permanent magnets are arranged in such a manner thateach center of gravity of the edge faces having the approximately squareshape is matched with a lattice point of a tetragonal lattice, a certainside of sides forming one of the edge faces of the plural permanentmagnets disposed in a certain row of the tetragonal lattice and acertain side of sides forming one of the edge faces of the other pluralpermanent magnets disposed in the same row of the tetragonal lattice isin a same straight line, all the edge faces having the square shapes ofthe permanent magnets are placed in an approximately same single plane,and any two of the polarities of the magnetic poles of the permanentmagnets disposed adjacent each other and spaced by the shortest routeare different each other; and

[0027] the yoke comprises plural through holes each of which has a shapewhich is the approximately same as the sectional shape which isapproximately square and the holes being arranged at the positions wherethe permanent magnets are disposed, and the yoke being arranged in sucha manner that the same single plane in which all the edge faces of thepermanent magnets are placed is disposed between an upper surface and alower surface of the yoke when the permanent magnets are inserted intothe through holes.” can preferably be used to magnetize the biasmagnetic films and the like of the magnetic sensor mentioned above.

[0028] The magnet array has the yoke formed of the magnetic material,and therefore, it can lead magnetic flux lines from the permanentmagnets to desirable portions. Accordingly, it is possible to magnetizethe bias magnetic film of the magnetic sensor and the like efficientlyby the magnet array.

[0029] In this case, it is preferable that the yoke have throughopenings serving as air gaps formed between the through holes that areadjacent each other and that are spaced by a shortest route.

[0030] Since this magnet array has through openings serving air gapsbetween the through holes that are adjacent each other and that arespaced by a shortest route (the edge faces having poles whose polaritiesare different from (opposite) each other are inserted into those twothrough holes), the magnetic flux concentrates both in the throughopenings and in a space close to the through openings. In other words,this magnet array can provide a narrow space local region with amagnetic field whose magnitude is great and whose direction is stablyconstant. Therefore, it is possible to magnetize the bias magnetic filmof the magnetic sensor and the like efficiently by this magnet array.

[0031] It is also preferable that the yoke have openings at regions eachof which is surrounding a center of gravity of a square drawn by linesconnecting the lattice points of the tetragonal lattice in a plan view.This magnet array has not only above mentioned through openings but alsothe different openings.

[0032] The regions where the openings are formed is the regionsurrounding a center of gravity of a square drawn by lines connectingthe lattice points of the tetragonal lattice. This regions is wheremagnetic flux lines stemming from the poles cross (or collide) to oneanother and thus the magnetic fields are unstable. Therefore, since theopenings can eliminate instability of the magnetic field between poleshaving different polarities each other, the magnetic field can be madeto be more linear, and thus, the magnetic field is provided which ismore stable and whose magnitude is greater than the magnetic field forlocal regions in the neighborhood of the through openings. With thisreason, it is possible to magnetize the bias magnetic film of themagnetic sensor and the like efficiently by this magnet array. It isalso preferable that each of the through holes of the yoke have a squareportion having a square shape which is the approximately same as theshape of the sectional square shape of the permanent magnet in a planview and a margin portions swelling outwardly from the square at each ofcorners of the square portion. When forming the through hole, in theyoke, having a square shape by etching, if the corner of the throughhole is not completely etched, the permanent magnet may not be insertedinto the through hole, since the corners of the thorough hole may becomearc-like shapes. However, since the margin portions are etched in themagnet array mentioned above in forming the through holes by etching,the permanent magnet can be assuredly inserted into the through hole inthe magnet array.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above and other objects, aspects, features and advantages ofthe present invention will become more apparent from the followingdetailed description when taken in conjunction with the accompanyingdrawings, in which:

[0034]FIG. 1 is a plan view of a magnetic sensor in accordance with anembodiment of the present invention;

[0035]FIG. 2 is a schematic enlarged plan view of a first X-axis GMRelement shown in FIG. 1;

[0036]FIG. 3 is a schematic sectional view of the first X-axis GMRelement shown in FIG. 2 cut by a plane along a line 1-1 in FIG. 2;

[0037]FIG. 4 is a view showing a structure of a spin valve film of thefirst X-axis GMR element shown in FIG. 2;

[0038]FIG. 5 is a graph showing by a solid line a resistance change ofthe first X-axis GMR element shown in FIG. 1 for a magnetic fieldchanged in the X-axis direction and showing by a broken line aresistance change thereof for a magnetic field changed in the Y-axisdirection;

[0039]FIG. 6A is an equivalent circuit diagram of an X-axis magneticsensor included in the magnetic sensor shown in FIG. 1;

[0040]FIG. 6B is a graph showing a change of output for the magneticfield changed in the X-axis direction of the X-axis magnetic sensor;

[0041]FIG. 7A is an equivalent circuit diagram of a Y-axis magneticsensor included in the magnetic sensor shown in FIG. 1;

[0042]FIG. 7B is a graph showing a change of output for the magneticfield changed in the Y-axis direction of the Y-axis magnetic sensor;

[0043]FIG. 8A is another equivalent circuit diagram of an X-axismagnetic sensor included in the magnetic sensor shown in FIG. 1;

[0044]FIG. 8B is a graph showing a change of output for the magneticfield changed in the X-axis direction of the X-axis magnetic sensor;

[0045]FIG. 9A is another equivalent circuit diagram of a Y-axis magneticsensor included in the magnetic sensor shown in FIG. 1;

[0046]FIG. 9B is a graph showing a change of output for the magneticfield changed in the Y-axis direction of the Y-axis magnetic sensor;

[0047]FIG. 10 is a plan view of a quartz glass, during a process forfabricating the magnetic sensor shown in FIG. 1, having the spin valvefilm formed thereon;

[0048]FIG. 11 is a plan view showing a metal plate for preparing amagnet array used upon fabricating the magnetic sensor shown in FIG. 1and a permanent bar magnet inserted into the metal plate;

[0049]FIG. 12 is a sectional view of the magnet array used uponfabricating the magnetic sensor shown in FIG. 1;

[0050]FIG. 13 is a perspective view wherein a part of a magnet of themagnet array shown in FIG. 12 is taken out;

[0051]FIG. 14 is a view showing one of processes for fabricating themagnetic sensor shown in FIG. 1;

[0052]FIG. 15 is a conceptional view showing a method of magnetizing abias magnet film of each GMR element of the magnetic sensor shown inFIG. 1;

[0053]FIG. 16 is a conceptional view showing a method of pinning adirection of magnetization in the pinned layer of each GMR element ofthe magnetic sensor shown in FIG. 1;

[0054]FIGS. 17A, 17B, 17C and 17D are plan views each showing a state ofmagnetization of the free layer and the bias magnet films of the GMRelement, wherein FIG. 17A is a view showing a state of the bias magnetfilms before they are magnetized, FIG. 17B is a view showing a state ofthe bias magnet films after they are magnetized, FIG. 17C is a viewshowing a state in which an external magnetic field is applied and FIG.17D is a view showing a state after the external magnetic field iseliminated;

[0055]FIG. 18A is a graph showing a resistance change, for the externalmagnetic field, of the GMR element in a state before the bias magnetfilms are magnetized;

[0056]FIG. 18B is a graph showing a resistance change, for the externalmagnetic field, of the GMR element in a state after the bias magnetfilms are magnetized;

[0057]FIGS. 19A, 19B and 19C are plan views each showing a state ofmagnetization of the free layer and the bias magnet films of the GMRelement, wherein FIG. 19A is a view showing a state of the bias magnetfilms before they are magnetized and that the external magnetic field isnot applied, FIG. 19B is a view showing a state in which a strongexternal magnetic field is applied and FIG. 19C is a view showing astate after the strong external magnetic field is eliminated;

[0058]FIG. 20 is a schematic enlarged plan view of a first X-axis GMRelement of a magnetic sensor according to another embodiment of thepresent invention;

[0059]FIG. 21 is a plan view of a magnetic sensor (N-type) in accordancewith another embodiment of the present invention;

[0060]FIG. 22 is a plan view of a magnetic sensor (S-type) in accordancewith another embodiment of the present invention;

[0061]FIG. 23 is a fragmentary plan view of the yoke of the magnet arrayMB in accordance with the present invention;

[0062]FIG. 24 is a fragmentary enlarged plan view of the yoke shown inFIG. 23;

[0063]FIG. 25 is a sectional view of the yoke shown in FIG. 24 cut by aplane along a line 2-2 in FIG. 24;

[0064]FIG. 26 is a plan view of a through hole of the yoke shown in FIG.23;

[0065]FIG. 27 is a sectional view of a substrate for the magnet array MBin accordance with the present invention;

[0066]FIG. 28 is a fragmentary plan view of the substrate for the arrayshown in FIG. 27;

[0067]FIG. 29 is a sectional view of a thin plate which will become thesubstrate for the array shown in FIG. 27;

[0068]FIG. 30 is a view showing one of processes for fabricating themagnet array MB;

[0069]FIG. 31 is a view showing one of processes for fabricating themagnet array MB;

[0070]FIG. 32 is a view showing one of processes for fabricating themagnet array MB;

[0071]FIG. 33 is a view showing one of processes for fabricating themagnet array MB;

[0072]FIG. 34 is a perspective view wherein a part of a magnet of themagnet array MB and the yoke are taken out;

[0073]FIG. 35 is a fragmentary sectional view of the magnet array MB;

[0074]FIG. 36 is a conceptional plan view of the magnet array MB toexplain a magnetic field by the magnet array MB;

[0075]FIG. 37 is a conceptional plan view of the magnet array MA toexplain a magnetic field by the magnet array MA;

[0076]FIG. 38 is a conceptional view showing a method of pinning adirection of magnetization in the pinned layer of each GMR element ofthe magnetic sensor shown in FIGS. 21 and 22;

[0077]FIG. 39 is a sectional view showing a relative positionalrelationship between a substrate and the magnet array MB whenmagnetizing the bias magnet file of each GMR element of the magneticsensor shown in FIGS. 21 and 22; and

[0078]FIG. 40 is a conceptional view showing a method of magnetizing abias magnet film of each GMR element of the magnetic sensor shown inFIGS. 21 and 22.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0079] Embodiments of a magnetic sensor in accordance with the presentinvention will now be described with reference to the drawings. Thismagnetic sensor is classified into N-type and S-type depending upon aproduction process described later. FIG. 1 is a plan view wherein anN-type magnetic sensor 10 and an S-type magnetic sensor 50 are placedside by side. The N-type magnetic sensor 10 and the S-type magneticsensor 50 have substantially the same shape and same configurationexcept that a direction of fixed magnetization in a pinned layer shownby black-solid arrows in FIG. 1 and a direction of magnetization in aninitial state in a free layer shown by outline arrows in FIG. 1 aredifferent from each other. Accordingly, the following explanation ismainly focused on the N-type magnetic sensor 10.

[0080] The magnetic sensor 10 comprises, as shown in FIG. 1, a singlechip (a single substrate or a monolithic chip) 10 a made of a quartzglass, which has a rectangular shape (almost square shape) viewed in aplane having sides along an X-axis direction and Y-axis directionperpendicular to each other, and has a little thickness in a Z-axisdirection perpendicular to the X-axis and Y-axis, plural insulatinglayers 10 b (wiring layers are included in this insulating layers)laminated on the substrate 10 a shown in FIG. 3, a total of eight GMRelements 11 to 14, 21 to 24 formed on the uppermost layer 10 b 1 of theinsulating layers 10 b and a total of eight initializing coils (coilsfor initializing) 31 to 34 and 41 to 44.

[0081] The first X-axis GMR element 11 is formed at a portion a littledownward from the almost central part in the Y-axis direction of thechip 10 a and in the vicinity of an end portion of the X-axis negativedirection. The direction of pinned magnetization of the pinned layer ofthe GMR element 11 is in the X-axis negative direction as shown by ablack-solid arrow in FIG. 1. The second X-axis GMR element 12 is formedat a portion a little upward from the almost central part in the Y-axisdirection of the chip 10 a and in the vicinity of the end portion of theX-axis negative direction. The direction of pinned magnetization of thepinned layer of the GMR element 12 is in the X-axis negative directionshown by a black-solid arrow in FIG. 1. The third X-axis GMR element 13is formed at a portion a little upward from the almost central part inthe Y-axis direction of the chip 10 a and in the vicinity of an endportion of the X-axis positive direction. The direction of pinnedmagnetization of the pinned layer of the GMR element 13 is in the X-axispositive direction as shown by a black-solid arrow in FIG. 1. The fourthX-axis GMR element 14 is formed at a portion a little downward from thealmost central part in the Y-axis direction of the chip 10 a and in thevicinity of the end portion of the X-axis positive direction. Thedirection of pinned magnetization of the pinned layer of the GMR element14 is in the X-axis positive direction shown by a black-solid arrow inFIG. 1.

[0082] The first Y-axis GMR element 21 is formed at a portion a littleleftward from the almost central part in the X-axis direction of thechip 10 a and in the vicinity of an end portion of the Y-axis positivedirection. The direction of pinned magnetization of the pinned layer ofthe GMR element 21 is in the Y-axis positive direction as shown by ablack-solid arrow in FIG. 1. The second Y-axis GMR element 22 is formedat a portion a little rightward from the almost central part in theX-axis direction of the chip 10 a and in the vicinity of the end portionof the Y-axis positive direction. The direction of pinned magnetizationof the pinned layer of the GMR element 22 is in the Y-axis positivedirection shown by a black-solid arrow in FIG. 1. The third Y-axis GMRelement 23 is formed at a portion a little rightward from the almostcentral part in the X-axis direction of the chip 10 a and in thevicinity of an end portion of the Y-axis negative direction. Thedirection of pinned magnetization of the pinned layer of the GMR element23 is in the Y-axis negative direction as shown by a black-solid arrowin FIG. 1. The fourth Y-axis GMR element 24 is formed at a portion alittle leftward from the almost central part in the X-axis direction ofthe chip 10 a and in the vicinity of the end portion of the Y-axisnegative direction. The direction of pinned magnetization of the pinnedlayer of the GMR element 24 is in the Y-axis negative direction shown bya black-solid arrow in FIG. 1.

[0083] Each of the GMR elements 11 to 14 and 21 to 24 has substantiallythe same structure except for the position on the chip 10 a. Therefore,the first X-axis GMR element 11 is taken as a representative examplehereinbelow for explaining the structure thereof.

[0084] The first X-axis GMR element 11 comprises, as shown in FIG. 2that is a plan view and FIG. 3 that is a schematic sectional view of thefirst X-axis GMR element 11 cut by a plane along a line of 1-1 in FIG.2, a plurality of narrow zonal portions 11 a . . . 11 a made of a spinvalve film SV and having a longitudinal direction in the Y-axisdirection and bias magnet films (hard ferromagnetic thin film layer andbecome a permanent magnet film by magnetization) 11 b . . . 11 b thatare made of hard ferromagnetic materials, having high coercive force andhigh squareness ratio, such as CoCrPt. Each of the narrow zonal portions11 a . . . 11 a extends in the X-axis direction on the upper surface ofeach of the bias magnet films 11 b . . . 11 b, and joins to the adjacentnarrow zonal portion 11 a to thereby form a so-called “zig-zag shape” aswell as to thereby magnetically join to each of the bias magnet films 11b . . . 11 b at the upper surface of each of the bias magnet films 11 b. . . 11 b.

[0085] As shown in FIG. 4 that illustrates the film structure, the spinvalve film SV of the first X-axis GMR element 11 includes a free layerF, a conductive spacer layer S made of Cu having a thickness of 2.4 nm(24A), a fixed layer (pin layer) P and a capping layer C made oftitanium (Ti) or tantalum (Ta) having a thickness of 2.5 nm (25A), whichare laminated in this order on the chip 10 a serving as a substrate.

[0086] The free layer F is a layer whose magnetization direction variesin accordance with the direction of the external magnetic field, andcomprises a CoZrNb amorphous magnetic layer 11-1 formed directly on thesubstrate 10 a and having a film thickness of 8 nm (80A), a NiFemagnetic layer 11-2 formed on the CoZrNb amorphous magnetic layer 11-1and having a film thickness of 3.3 nm (33A), and a CoFe layer 11-3formed on the NiFe magnetic layer 11-2 and having a film thickness ofapproximately 1 to 3 nm (10 to 30A). The CoZrNb amorphous magnetic layer11-1 and NiFe magnetic layer 11-2 constitute a soft ferromagneticmaterial thin film layer. The CoFe layer 11-3 prevents Ni of the NiFemagnetic layer 11-2 and Cu 11-4 of the spacer layer S from diffusing.

[0087] The fixed layer (pin layer) P is made by superposing a CoFemagnetic layer 11-5 having a film thickness of 2.2 nm (22A), and anantiferromagnetic film 11-6 which is formed of a PtMn alloy including 45to 55 mol % of Pt and has a film thickness of 24 nm (240A). The CoFemagnetic layer 11-5 is in an exchange coupling manner to the magnetizedantiferromagnetic film 11-6. Thus, the direction of magnetization(magnetizing vector) of the CoFe magnetic layer 11-5 is pinned (fixed)in the X-axis negative direction as described above.

[0088] The bias magnet films 11 b . . . 11 b gives a bias magnetic fieldto the free layer F in the Y-axis negative direction (the directionshown by the outline arrow in FIGS. 1 and 2) that is the longitudinaldirection of the free layer F in order to maintain uniaxial anisotropyof the free layer F.

[0089] The first X-axis GMR element 11 thus configured presents aresistance value, which changes in almost proportion to the externalmagnetic field that changes along the X-axis within a range of −Hc to+Hc, as indicated by the solid line of FIG. 5, and presents an almostconstant resistance value to the external magnetic field that changesalong the Y-axis, as indicated by the broken line of FIG. 5.

[0090] Subsequently, the initializing coils 31 to 34 and 41 to 44 areexplained. The initializing coils 31 to 34 and 41 to 44 are buried inthe lower insulating layer 10 b 2 under the uppermost layer 10 b 1 ofthe insulating layers. The initializing coils 31 to 34 and 41 to 44 arepositioned approximately immediately below each of the GMR elements 11to 14 and 21 to 24, respectively. Each of the initializing coils 31 to34 and 41 to 44 has the same shape to one another, and its relativepositional relationship to the corresponding GMR element immediatelyabove each coil is the same to one another. Each of the initializingcoils 31 to 34 and 41 to 44 applies the initializing magnetic field inthe direction shown by the outline arrow in FIG. 1 to each correspondingGMR element.

[0091] The following explanation is made by taking the initializing coil31 as a representative example. This initializing coil 31 is wound so asto have an approximately rectangular outer shape viewed in a plane, andcomprises plural initializing magnetic field generating sections 31 a .. . 31 a extending linearly in the direction (X-axis direction)perpendicular to the longitudinal direction of the narrow zonal portions11 a of the first X-axis GMR element 11 at a region immediately belowthe first X-axis GMR element 11 viewed in a plane. Further, one end 31 band the other end 31 c of the initializing coil 31 are connected to apositive polarity and negative polarity of a constant voltage sourcerespectively. When a predetermined condition is established,predetermined current is made to flow through the initializing coil 31,thereby applying the initializing magnetic field in the Y-axis negativedirection to the narrow zonal portion 11 a of the first X-axis GMRelement 11 as shown by the outline arrow in FIG. 1.

[0092] Subsequently explained are an X-axis magnetic sensor (a magneticsensor with a magnetic field detecting direction which is the X-axisdirection) and a Y-axis magnetic sensor (a magnetic sensor with amagnetic field detecting direction which is the Y-axis direction)composed respectively of the GMR elements 11 to 14 and 21 to 24. Asshown by an equivalent circuit in FIG. 6A, the X-axis magnetic sensor isformed such that the first to fourth X-axis GMR elements 11 to 14 arefull-bridge-connected via a conductor not shown in FIG. 1. In FIG. 6A,each graph shown at the position adjacent to each of the first to fourthGMR elements 11 to 14 indicates a characteristic (change in theresistance value R with respect to the external magnetic field) of theGMR element adjacent to each graph. This is also true in FIGS. 7 to 9.Symbols Hx and Hy in these graphs respectively indicate the externalmagnetic field whose magnitude varies along the X-axis and Y-axis.

[0093] In this configuration, a connection point between the firstX-axis GMR element 11 and the fourth X-axis GMR element 14 and aconnection point between the second X-axis GMR element 12 and the thirdX-axis GMR element 13 are respectively connected to the positivepolarity and the negative polarity (ground) of the constant voltagesource, whereby a potential of +V (5 (V) in this embodiment) and apotential −V (0 (V) in this embodiment) are respectively appliedthereto. Then, a difference in potential V_(0X) between a connectionpoint of the first X-axis GMR element 11 and the third X-axis GMRelement 13 and a connection point of the fourth X-axis GMR element 14and the second X-axis GMR element 12 are taken out as a sensor output.As a result, the X-axis magnetic sensor outputs, as shown in FIG. 6B, anoutput voltage V_(ox) that varies in approximately proportion to theexternal magnetic field Hx that changes along the X-axis.

[0094] As shown by an equivalent circuit in FIG. 7A, the Y-axis magneticsensor is formed such that the first to fourth Y-axis GMR elements 21 to24 are full-bridge-connected via a conductor not shown in FIG. 1. Aconnection point between the first Y-axis GMR element 21 and the fourthY-axis GMR element 24 and a connection point between the second Y-axisGMR element 22 and the third Y-axis GMR element 23 are respectivelyconnected to the positive polarity and the negative polarity (ground) ofthe constant voltage source, whereby a potential of +V (5 (V) in thisembodiment) and a potential of −V (0 (V) in this embodiment) arerespectively applied thereto. Then, a difference in potential V_(0y)between a connection point of the first Y-axis GMR element 21 and thethird Y-axis GMR element 23 and a connection point of the fourth Y-axisGMR element 24 and the second Y-axis GMR element 22 are taken out as asensor output. As a result, the Y-axis magnetic sensor outputs, as shownin FIG. 7B, an output voltage V_(oy) that varies in approximatelyproportion to the external magnetic field Hy that changes along theY-axis. The above description is about the configuration of the N-typemagnetic sensor 10.

[0095] On the other hand, the S-type magnetic sensor 50 includes GMRelements 51 to 54 and 61 to 64 and initializing coils 71 to 74 and 81 to84 as shown in FIG. 1. The S-type magnetic sensor 50 has thesubstantially same structure as that of the magnetic sensor 10 andincludes the X-axis magnetic sensor and Y-axis magnetic sensor.

[0096] Specifically, as shown by an equivalent circuit in FIG. 8A, theX-axis magnetic sensor is formed such that the first to fourth X-axisGMR elements 51 to 54 are full-bridge-connected via a conductor notshown in FIG. 1. In this configuration, a connection point between thefirst X-axis GMR element 51 and the fourth X-axis GMR element 54 and aconnection point between the second X-axis GMR element 52 and the thirdX-axis GMR element 53 are respectively connected to the positivepolarity and the negative polarity (ground) of the constant voltagesource, whereby a potential of +V (5 (V) in this embodiment) and apotential of −V (0 (V) in this embodiment) are respectively appliedthereto. Then, a difference in potential V_(0X) between a connectionpoint of the first X-axis GMR element 51 and the third X-axis GMRelement 53 and a connection point of the fourth X-axis GMR element 54and the second X-axis GMR element 52 are taken out as a sensor output.As a result, the X-axis magnetic sensor outputs, as shown in FIG. 8B, anoutput voltage V_(ox) that varies in approximately proportion to theexternal magnetic field Hx that changes along the X-axis.

[0097] Further, as shown by an equivalent circuit in FIG. 9A, the Y-axismagnetic sensor of the magnetic sensor 50 is formed such that the firstto fourth Y-axis GMR elements 61 to 64 are full-bridge-connected via aconductor not shown in FIG. 1. A connection point between the firstY-axis GMR element 61 and the fourth Y-axis GMR element 64 and aconnection point between the second Y-axis GMR element 62 and the thirdY-axis GMR element 63 are respectively connected to the positivepolarity and the negative polarity (ground) of the constant voltagesource, whereby a potential of +V (5 (V) in this embodiment) and apotential −V (0 (V) in this embodiment) are respectively appliedthereto. Then, a difference in potential V_(0y) between a connectionpoint of the first Y-axis GMR element 61 and the third Y-axis GMRelement 63 and a connection point of the fourth Y-axis GMR element 64and the second Y-axis GMR element 62 are taken out as a sensor output.As a result, the Y-axis magnetic sensor outputs, as shown in FIG. 9B, anoutput voltage V_(0y) that varies in approximately proportion to theexternal magnetic field Hy that changes along the Y-axis.

[0098] Subsequently explained is a process for manufacturing themagnetic sensors 10 and 50 thus configured as described above. Firstly,each insulating layer 10 b is laminated on a rectangular quartz glass(wafer) 10 a 1, that becomes the substrates 10 a and 50 a later, withthe formation of a predetermined wiring or LSI, followed by forming theinitializing coils 31 to 34, 41 to 44, 71 to 74 and 81 to 84 in theinsulating layer 10 b 2, and then, the uppermost insulating layer 10 bis formed (see FIGS. 1 to 3).

[0099] Then, plural films M composing the GMR elements 11 to 14, 21 to24, 51 to 54 and 61 to 64 are formed like an island. Specifically, saidbias films 11 b are formed and said films M which will become GMRelements 11 to 14, 21 to 24, 51 to 54 and 61 to 64 are formed on thebias film 11 b. This film formation is performed by using a ultra-highvacuum device in a manner of continuous laminating with a precisethickness. The films M are patterned and thereby plural island-likeportions which will become the GMR elements are formed. These films Mare formed to be arranged at each position of the GMR elements 11 to 14,21 to 24, 51 to 54 and 61 to 64 shown in FIG. 1 when the quarts glass 10a 1 is cut along the broken line in FIG. 10 by a subsequent cuttingprocess to thereby be divided into the individual magnetic sensor 10 and50 shown in FIG. 1.

[0100] Subsequently, as shown in FIG. 11 that is a plan view, arectangular metal plate 91 is prepared that is provided only with pluralsquare through-holes arranged in a tetragonal lattice (i.e., squarethrough-holes each having sides parallel to the X-axis and Y-axis arearranged along the X-axis and Y-axis so as to be spaced at equalintervals). Each of permanent bar magnets 92 . . . 92 with a shape of arectangular parallelepiped having a square section approximately equalto each through-hole is inserted into each through-hole such that theedge face having a magnetic pole of the permanent bar magnet 92 . . . 92formed thereon becomes parallel to the metal plate 91. At this time, thepermanent bar magnets 92 . . . 92 are arranged such that the polarity ofthe magnetic pole is different from the adjacent polarity by theshortest route in a plane including each edge face of the permanent barmagnets 92 . . . 92. It is to be noted that each of the used permanentbar magnets 92 . . . 92 has magnetic charge whose magnitude isapproximately equal to one another.

[0101] Then, as shown in FIG. 12 that represents a section along X-Zplane, a plate 92 is prepared that is made of a transparent quartz glasshaving a thickness of about 0.5 mm and having a rectangular shapeapproximately equal to the metal plate 91. Thereafter, the upper surface(the surface opposite to the edge face on which the magnetic pole isformed) of the permanent bar magnets 92 . . . 92 and the bottom surfaceof the plate 93 are bonded by an adhesive, and then, the metal plate 91is removed from below. At this stage, a magnet array MA is formed by thepermanent bar magnets 92 . . . 92 and the plate 93, wherein pluralpermanent magnets, each having an approximately rectangularparallelepiped shape in which the sectional shape perpendicular to onecentral axis of the rectangular parallelepiped is approximately square,are arranged such that the center of gravity of the edge face havingapproximately square shape is matched with a lattice point of thetetragonal lattice, and the polarity of the magnetic pole of eachpermanent magnet thus arranged is different from the polarity of themagnetic pole of the adjacent other permanent magnet spaced by theshortest route.

[0102]FIG. 13 is a perspective view showing a state wherein only fourpermanent bar magnets 92 . . . 92 are taken out. As apparent from thisfigure, there are magnetic fields formed on the edge face (the edge faceon which the magnetic pole is formed) of the permanent bar magnet 92 . .. 92, the magnetic fields from one N-pole directing to the S-polesadjacent to this N-pole by the shortest route and each having adifferent direction at an angle of 90 degrees. In this embodiment, thismagnetic field is used as a magnetic field for magnetizing each biasmagnet film 11 b to 14 b, 21 b to 24 b, 51 b to 54 b and 61 b to 64 b ofeach GMR element 11 to 14, 21 to 24, 51 to 54 and 61 to 64 and as amagnetic field for fixing the direction of magnetization in each fixedlayer P (pinned layer in the fixed layer P).

[0103] Specifically, as shown in FIG. 14, the quartz glass 10 a 1 onwhich the film M which will become the GMR element is formed is firstlyarranged such that the face having the film M which will become the GMRelement formed thereon comes in contact with the upper surface of theplate 93, and then, the plate 93 and the quartz glass 10 a 1 are fixedto each other by a cramp C. At this time, as shown in FIG. 15 that is aplan view for enlarging the section that becomes later the magneticsensors 10 and 50 by paying attention to the section corresponding totwo of the magnetic sensors 10 and 50, the quartz glass 10 a 1 and themagnet array MA are relatively arranged such that each cross-point CP ofthe cutting plane line CL of the quartz glass 10 a 1 that becomes eachside of the magnetic sensors 10 and 50 is matched with the respectivecenter of gravity of the permanent bar magnets 92 . . . 92. Accordingly,as shown by arrows in FIG. 15, a magnetic field is applied to each filmM which will become the GMR element in the longitudinal direction of thenarrow zonal portion of each film M in the state wherein the quartzglass 10 a 1 is placed on the upper surface of the plate 93.

[0104] The present embodiment utilizes this magnetic field formagnetizing the bias magnet films 11 b to 14 b, 21 b to 24 b, 51 b to 54b and 61 b to 64 b as well as for matching the direction ofmagnetization in each magnetic domain in the free layer F with thedirection in the initial state. That is, magnetization in each magneticdomain in the free layer F is initialized.

[0105] Subsequently, the relative relationship between the quartz glass10 a 1 having the film M which will become the GMR element formedthereon and the magnet array MA (plate 93) is changed as shown in a planview of FIG. 16, whereby the surface on which the film M which willbecome the GMR element is formed is arranged to be brought into contactwith the upper surface of the plate 93. At this time, the quartz glass10 a 1 and the magnet array MA are relatively arranged such that eachcross-point of the cutting plane line CL of the quartz glass 10 a 1 thatbecomes each side of the magnetic sensors 10 and 50 is matched with therespective center of gravity of the four adjacent permanent bar magnets92 . . . 92. Accordingly, as shown by arrows in FIG. 16, a magneticfield is applied to each film M which will become the GMR element in thedirection perpendicular to the longitudinal direction of the narrowzonal portion of each film M in the state wherein the quartz glass 10 a1 is placed on the upper surface of the plate 93.

[0106] The present embodiment utilizes this magnetic field forperforming a heat treatment (annealing for ordering) to fix thedirection of magnetization in the fixed layer P (pinned layer of thefixed layer P). Specifically, the plate 93 and the quartz glass 10 a 1are fixed to each other by the cramp C with the state shown in FIG. 16,then, the resultant is heated in a vacuum to 250 to 280° C. and left forabout four hours in this state.

[0107] Thereafter, the quartz glass 10 a 1 is removed to form a wiringor the like for connecting each film M, and finally, the quartz glass 10a 1 is cut along the broken line (or the cutting line CL) shown in FIG.10 etc. As described above, a great number of magnetic sensors 10 and 50shown in FIG. 1 are simultaneously produced.

[0108] As described above, a magnetic sensor according to the embodimentof the present invention has bias magnet films 11 b . . . 11 b providedat both ends of the free layer F in the longitudinal direction forproducing in the free layer a bias magnetic field in a predetermineddirection (in the longitudinal direction of the free layer), whereby thedirection of magnetization in each magnetic domain in the free layer canstably be maintained in the predetermined direction when an externalmagnetic field is not present.

[0109] Further, the initializing coils 31 to 34 and 41 to 44 areenergized under a predetermined condition to thereby generate aninitializing magnetic field for returning the direction of magnetizationin each magnetic domain in the free layer to the direction (i.e., thelongitudinal direction of the free layer) same as the direction of thebias magnetic field by the bias magnet films, whereby the direction ofmagnetization in each magnetic domain in the free layer can assuredly bereturned to the initial state even if the direction of magnetization isdisturbed by applying a strong magnetic field to the free layer. As aresult, a hysteresis that occurs when the external magnetic field is inthe vicinity of “0” with respect to the change of the external magneticfield can be maintained small of the magnetic sensors 10 and 50. Thus,the magnetic sensor is capable of detecting a minute magnetic field withhigh precision over a long period.

[0110] Further, according to the production process of the magneticsensor according to the embodiment of the present invention, there isprepared a magnet array MA that is configured such that plural permanentmagnets are arranged at a lattice point of a tetragonal lattice and thepolarity of the magnetic pole of each permanent magnet is different fromthe polarity of the other adjacent magnetic pole spaced by the shortestroute. Therefore, the direction of magnetization in each magnetic domainin the free layer is initialized and the bias magnet films aremagnetized, and further, a pinning is performed by pinning the directionof magnetization in the magnetic layer that becomes a pinned layer.Accordingly, plural GMR elements having different magnetic fielddetecting directions (perpendicular to each other) can easily andefficiently be formed on a single chip, thereby being capable ofmanufacturing with low cost a magnetic sensor of a single chip which iscapable of detecting at least respective magnetic fields whose magnitudeis changed in the directions perpendicular to each other.

[0111] It should be noted that, in the above embodiment, the films M forGMR films (films M which will be the GMR elements) are formed after thebias films (films for magnets) are patterned, and the films M for GMRfilms are annealed for ordering after the GMR films are patterned.However, the annealing process for ordering can be performed before thefilms M for GMR films are patterned. Further, the bias films can beformed after the films M for GMR films are formed.

[0112] Next, another embodiment of a magnetic sensor (second embodiment)in accordance with the present invention will be described. Thismagnetic sensor is also classified into N-type shown in FIG. 21 which isa plan view of the N-type sensor and S-type shown in FIG. 22 which is aplan view of the S-type sensor. The N-type magnetic sensor 110 and theS-type magnetic sensor 150 have substantially the same shape and sameconfiguration except that a direction of fixed magnetization in a pinnedlayer shown by black-solid arrows in FIGS. 21 and 22 and a direction ofmagnetization in an initial state in a free layer shown by outlinearrows in FIGS. 21 and 22 are different from each other. Note that,initializing coils are omitted in FIGS. 21 and 22.

[0113] The N-type magnetic sensor 110 has the same structure as theN-type magnetic sensor 10 except the position of the GMR elements andthe initializing coils. The N-type magnetic sensor 110 comprises asingle chip 110 a which is the same as the single chip 10 a, insulatinglayers which is the same as the insulating layers 10 b, a total of eightGMR elements 111 to 114, 121 to 124 formed on the uppermost layer of theinsulating layers and a total of eight initializing coils (coils forinitializing). A relative positional relationship between the GMRelements 111 to 114, 121 to 124 and the eight initializing coils is thesame as that between the GMR elements 11 to 14, 21 to 24 and theinitializing coils 31 to 34, 41 to 44. The GMR elements 111 to 114 forman X-axis magnetic sensor by being full-bridge-connected similarly tothe GMR elements 11 to 14. The GMR elements 121 to 124 form an Y-axismagnetic sensor by being full-bridge-connected similarly to the GMRelements 21 to 24.

[0114] The first X-axis GMR element 111 is formed at an almost centralportion in the Y-axis direction of the chip 110 a and in the vicinity ofan end portion of the X-axis negative direction. The second X-axis GMRelement 112 is formed at an almost central portion in the Y-axisdirection of the chip 110 a and at a portion spaced by a predeterminedshort distance in the X-axis positive direction from the first X-axisGMR element 111. The third X-axis GMR element 113 is formed at an almostcentral portion in the Y-axis direction of the chip 110 a and in thevicinity of an end portion of the X-axis positive direction. The fourthX-axis GMR element 114 is formed at an almost central portion in theY-axis direction of the chip 110 a and at a portion spaced by apredetermined short distance in the X-axis negative direction from thethird X-axis GMR element 113. An each of longitudinal directions of thefirst to fourth X-axis GMR elements 111 to 114 is parallel to the Y-axisdirection.

[0115] The first Y-axis GMR element 121 is formed at an almost centralportion in the X-axis direction of the chip 110 a and in the vicinity ofan end portion of the Y-axis positive direction. The second Y-axis GMRelement 122 is formed at an almost central portion in the X-axisdirection of the chip 110 a and at a portion spaced by a predeterminedshort distance in the Y-axis negative direction from the first Y-axisGMR element 121. The third Y-axis GMR element 123 is formed at an almostcentral portion in the X-axis direction of the chip 110 a and in thevicinity of an end portion of the Y-axis negative direction. The fourthY-axis GMR element 124 is formed at an almost central portion in theX-axis direction of the chip 110 a and at a portion spaced by apredetermined short distance in the Y-axis positive direction from thethird Y-axis GMR element 123. An each of longitudinal directions of thefirst to fourth Y-axis GMR elements 121 to 124 is parallel to the X-axisdirection.

[0116] The S-type magnetic sensor 150 has the same structure as theS-type magnetic sensor 50 except the position of the GMR elements andthe initializing coils. The magnetic sensor 150 comprises a single chip150 a which is the same as the single chip 50 a, insulating layers whichis the same as the insulating layers 10 b, a total of eight GMR elements151 to 154, 161 to 164 formed on the uppermost layer of the insulatinglayers and a total of eight initializing coils (coils for initializing).A relative positional relationship between the GMR elements 151 to 154,161 to 164 and the eight initializing coils is the same as that betweenthe GMR elements 51 to 54, 61 to 64 and the initializing coils 71 to 74,81 to 84. The GMR elements 151 to 154 form an X-axis magnetic sensor bybeing full-bridge-connected similarly to the GMR elements 51 to 54. TheGMR elements 161 to 164 form an Y-axis magnetic sensor by beingfull-bridge-connected similarly to the GMR elements 61 to 64.

[0117] A positional relationship between the first to fourth X-axis GMRelements 151 to 154 and the substrate 150 a is the same as that betweenthe first to fourth X-axis GMR elements 111 to 114 and the substrate 110a. An each of longitudinal directions of the first to fourth GMRelements 151 to 154 is parallel to the Y-axis direction. A positionalrelationship between the first to fourth Y-axis GMR elements 161 to 164and the substrate 150 a is the same as that between the first to fourthY-axis GMR elements 121 to 124 and the substrate 110 a. An each oflongitudinal directions of the first to fourth GMR elements 161 to 164is parallel to the X-axis direction.

[0118] Subsequently explained is a process for manufacturing themagnetic sensors 110 and 150 thus configured as described above. In thisprocess, the magnet array MA described above and a magnet array MB whichis different from the magnet array MA are used.

[0119] Firstly, the magnet array MA is prepared by the process mentionedabove and the magnet array MB is prepared by the following processbelow. Prior to the process to make the magnet array MB, each of partsthat constitute magnet array MB is explained. The magnet array MBcomprises a yoke (yoke plate) 200, a substrate for the array 210 andplural permanent magnets (permanent bar magnets) 230.

[0120] The yoke 200 is shown in FIGS. 23, 24 and 25. FIG. 23 is afragmentary plan view of the yoke 200, FIG. 24 is an enlarged plan viewof FIG. 23 and FIG. 25 is a sectional view of the yoke shown in FIG. 24cut by a plane along a line 2-2 in FIG. 24. This yoke 200 is a thinplate formed of magnetic material which has larger permeability than air(e.g., 42 alloy Fe-42Ni alloy and the like). Preferably, yoke 200 can beformed of high saturation-high permeability material such as permalloyor silicon steel (silicon sheet). The planar shape of the yoke isrectangle. The plate thickness of the yoke 200 is 0.15 mm in thisexample. The yoke 200 has plural thorough holes 201. The through hole201 has an approximately square shape viewed in a plane. The pluralthrough holes 201 are arranged in a tetragonal lattice. Specifically,the through holes 201 are disposed such that each center of gravity ofthe through holes 201 is matched with a lattice point SP of thetetragonal lattice shown in FIG. 24. As viewed in a plane, a certainside of sides forming the through hole 201 is parallel to a certain sideof sides forming the adjacent through hole 201. In other words, acertain side of sides forming the through hole 201 and a certain side ofsides forming other through hole 201 located on the same row (or column)of the tetragonal lattice are on (in) a same straight line.

[0121] Each of the through holes 201, as shown in FIG. 26 showing aplanar shape of the through hole 201, has a shape composed of a squareportion 201 a and margin portions (circle arc portions or R portions)201 b viewed in a plane. A shape of the square portion 201 a is asquare. The margin portion 201 b swells outwardly from the square ateach of corners of the square portion 201 a. Specifically, an outershape (outline) of the margin portion 201 b is a circle arc whose centerPR is on a diagonal line CR of the square portion 201 a.

[0122] Through openings 202 serving as air gaps are formed between thethrough hole 201 and the other adjacent through hole 201 spaced by theshortest route from the former through hole 201 (i.e., between throughholes 201, 201 that are adjacent each other with a shortest distance). Ashape of the through opening 202 is approximately a rectangle in viewedin a plane. A longer side of the through opening 202 is parallel to aside of the square portion 201 b of the through hole 201 next to thesame through opening 202. Length of the longer side of the throughopening 202 is approximately the same as or is slightly shorter thanlength of the side of the square portion 201 a. Length of the shorterside of the through opening 202 is longer than length of the longer side(side in the longitudinal direction) of each of the films M which willbecome GMR elements 111 to 114, 121 to 124, 151 to 154 and 161 to 164.

[0123] The yoke 200 has openings (openings for controlling magneticflux) 203. The opening 203, viewed in a plane, is formed at a regionsurrounding a center of gravity SQ of a square drawn by lines connectingthe lattice points of the tetragonal lattice. One of the openings 203has a shape of a circle whose center is on the center of gravity SQviewed in a plane.

[0124] The substrate for the array 210, shown in FIGS. 27 and 28, is asubstrate made by processing a thin plate 210 a, shown in FIG. 29,formed of magnetic material (e.g., permalloy). The substrate for thearray 210 has almost the same shape as the yoke 200 viewed in a plane.The substrate for the array 210 includes plural concavities (ditches)210 b. Plural concavities 210 b are formed at the same positions (samelocations) as the through holes 201 of the yoke 200. A shape of theconcavity 210 b is almost the same as the shape of the square portion201 a of the through hole 201.

[0125] The permanent bar magnets 230 has a shape of a rectangularparallelepiped shape (see. FIG. 31.). The permanent bar magnet 230 has asectional shape, perpendicular to one relatively longer central axis ofthe rectangular parallelepiped, which is an approximately square shapeapproximately same as the shape of the through hole 201 (and theconcavity 210 b). Poles of the permanent bar magnet 230 are formed atboth edge faces each of which has the square shape. Magnitude of each ofmagnetic charges of the plural permanent bar magnets 230 isapproximately equal to one another.

[0126] Subsequently explained is a process for manufacturing the magnetarray MB. Firstly, a thin plate which will become the yoke 200 isprepared. The through holes 201, the through openings 202 and theopenings 203 are formed in the thin plate by etching. Next, theconcavities 210 b are formed on the thin plate 210 a which will becomethe substrate for the array 210 by etching (by half-etching).

[0127] Next, square column-like spacers (bar) 220 are disposed on thesubstrate for the array 210, as shown in FIG. 30 which is a perspectiveview and in FIG. 31 which is a sectional view. The spacers 220 areplaced between one row constituted by the plural concavities 210 b andthe other row, constituted by the plural concavities 210 b, which isnext to and is parallel to the former row. When the spacers 220 arearranged in this manner, length of the spacer 220 along the Z-axisdirection is shorter than length between both edge faces having magneticpoles of the permanent bar magnet 230. Note that the margin portions 201b are omitted in FIG. 30.

[0128] Subsequently, the yoke 200 is placed (disposed or arranged) onthe spacers 220. At this time, the yoke 200 is arranged in such a mannerthat the through holes 201 (the square portions 201 a) of the yoke 200and the concavities 210 b of the substrate for the array 210 coincide ina plan view. In other words, in a state where the yoke 200 is disposedon the spacers 220, each of the concavities 210 b coincides with eachone of the through holes 201 in a Z-axis direction. Note that a mark fordetermining position of them (i.e., an alignment mark) may be formed onthe yoke 200 and the substrate for the array 210.

[0129] Next, each of the plural permanent bar magnets 230 is insertedinto each of the plural through holes 201. At the time of the insertionof the permanent bar magnets 230, one of the edge faces having magneticpoles of the permanent bar magnets 230 is made to be in abutment(contact) with each of upper surfaces of the concavities 210 b of thesubstrate for the array 210. As a result, the other edge faces havingmagnetic poles of the permanent bar magnets 230 (this face is alsosimply referred to as “upper surface” of the magnet 230 hereinafter) isplaced (disposed) in a same plane (on a single plane). Also, at thistime, in the plane where the upper surfaces of the magnet 230 isdisposed, a polarity of a magnet pole of each permanent magnet 230 isdifferent from (opposite to) a polarity of the other adjacent magnetpole spaced by the shortest route (i.e., shortest distance).Accordingly, the permanent bar magnet 230 is arranged as shown in FIG.23. In this stage, a movement of the permanent bar magnets 230 in a sidedirection (in a transverse direction) is prohibited because the magnets230 are inserted into both the through holes 201 of the yoke 200 and theconcavities 210 b.

[0130] Next, the yoke 200 is lifted upwardly (in the Z-axis positivedirection) by utilizing the openings 203 of the yoke 200. Morespecifically, two of the openings 203 are grasped with tweezers and theyoke 200 is lifted by the tweezers. This operation is repeated for theother openings 203 and the whole yoke is gradually lifted upward. Atthis time, as shown in FIG. 33, height of the yoke 200 (distance betweenthe yoke 200 and the substrate for the array 210) is adjusted in such amanner that the plane formed by the upper surfaces of the permanent barmagnets 230 (i.e., all the other edge faces having magnetic poles of thepermanent bar magnets 230) is placed between an upper surface 200 up ofthe yoke 200 and a lower surface 200 dn of the yoke 200. In other words,the yoke 200 is lifted upwardly such that the upper surface of thepermanent bar magnet 230 is made to be within plate thickness of theyoke 200. It should be noted that a plane formed by the upper surface200 up of the yoke 200 coincides with a plane formed by the uppersurfaces of the permanent bar magnets 230. Then, the spacers are takenout and the yoke 200 is fixed to the substrate for the array 210. Themagnet array MB is thus completed.

[0131]FIG. 34 is a perspective view showing a state wherein only fourpermanent bar magnets 230 . . . 230 are taken out. As is apparent fromthis figure, there are provided magnetic fields from one N-poledirecting to the S-poles adjacent to this N-pole by the shortest routeand each having a different direction at an angle of 90 degrees, abovethe upper surfaces (edge faces having the pole) of the permanent barmagnets 230 . . . 230. In this embodiment, this magnetic field given bythe magnet array MB is used as a magnetic field for magnetizing eachbias magnet film of each GMR element 111 to 114, 121 to 124, 151 to 154and 161 to 164.

[0132] This magnet array MB has through openings 202 serving as air gapsformed between two of (upper surfaces of) the permanent bar magnets 230that are spaced by the shortest route and next to each other. With thiscinfiguration, as shown in FIG. 35, magnetic flux concentrates both inthe through openings 202 and in a space close to the through openings202. In other words, the magnet array MB can provide a narrow spacelocal region with a magnetic field whose magnitude is great and whosedirection is stably constant.

[0133]FIGS. 36 and 37 show states of magnetic flux generated by themagnet array MB and the magnet array MA by arrows, respectively. Asunderstood by comparing one of the figures with the other figure, themagnet array MB has not only above mentioned through openings 202 butalso openings 203, and therefore, it can make the magnetic field formedbetween both the permanent bar magnets that are next to each other andare spaced by the shortest route more linear and can provide locally themagnetic field which is more stable and whose magnitude is greater thanthe magnetic field provided by the magnet array MA.

[0134] With these steps mentioned above, the magnet array MA and themagnet array MB are prepared. Therefore, the concrete process (method)for manufacturing (producing) the magnetic sensors 110 and 150 isexplained, hereinafter.

[0135] Firstly, a substrate (a quartz glass that will become a substrate110 a 1 described later with reference to FIG. 39, a wafer) is preparedon which films M, which will become the GMR elements 111 to 114, 121 to124, 151 to 154, 161 to 164, are formed. This substrate is formed in amanner similar to the substrate 10 a 1 shown in FIG. 10. These films Mare arranged in such a manner that, when this substrate is cut in thecutting process which will be carried out later, individual magneticsensors 110 and 150 shown in FIGS. 21 and 22 are obtained.

[0136] Next, the above mentioned substrate on which films M which willbecome the GMR elements are formed and the magnet array MA (the plate93) are arranged as shown in FIG. 38, and relative positionalrelationship between them is fixed. At this time, they are disposed insuch a manner that a surface on which the films M which will become theGMR elements are formed is made to come in contact with (be in abutmentwith) an upper surface of the plate 93 (see. FIG. 14.). Further, thesubstrate and the magnet array MA are relatively arranged in such amanner that each cross-point CP of the cutting plane line CL of thesubstrate that becomes each side of the magnetic sensors 110 and 150 ismatched with the respective center of gravity of the four adjacentpermanent bar magnets 92 . . . 92. As a result, a magnetic field isapplied to each film M which will become the GMR element in thedirection perpendicular to the longitudinal direction of the narrowzonal portion of each film M in the state wherein the substrate isplaced on the upper surface of the magnet array MA, as shown by arrowsin FIG. 38.

[0137] This second embodiment utilizes this magnetic field forperforming a heat treatment to fix the direction of magnetization in thefixed layer P (pinned layer of the fixed layer P). Specifically, theplate 93 and the substrate are fixed to each other by the cramp C (see.FIG. 14) with the state shown in FIG. 38, then, the resultant is heatedin a vacuum to 250 to 280° C. and left for about four hours in thisstate (i.e., the annealing for ordering is performed).

[0138] Next, as shown in FIG. 39, the substrate 110 a 1 on which thefilms M which will become the GMR elements are formed is arranged insuch a manner that the plane on which the films M which will become theGMR elements are formed comes in contact with (is in abutment with) theupper surface 200 up of the yoke 200 of the magnet array MB. At thistime, as shown in FIG. 40 which is a fragmentary enlarged plan view, thesubstrate and the magnet array MB are relatively arranged in such amanner that each cross-point CP of the cutting plane line CL of thesubstrate 110 a 1 that becomes each side of the magnetic sensors 110 and150 is matched with the respective center of gravity of the eachpermanent bar magnet 230 . . . 230. At this time, the films M which willbe the GMR elements is disposed inside of the through openings 202 ofthe yoke 200, in viewed in a plane. Accordingly, as shown by arrows inFIG. 40, a magnetic field is applied to each film M which will becomethe GMR element in the longitudinal direction of the narrow zonalportion of each film M in the state wherein the substrate 110 a 1 isplaced on the upper surface 200 up of the yoke 200.

[0139] This second embodiment utilizes this magnetic field formagnetizing the bias magnet films as well as for matching the directionof magnetization in each magnetic domain in the free layer F with thedirection in the initial state.

[0140] Thereafter, the substrate 110 a 1 is removed to form a wiring orthe like for connecting each film M, and finally, the substrate 110 a 1is cut along the broken line shown in FIGS. 38 and 40. As describedabove, a great number of monolithic (single chip) magnetic sensors 110shown in FIG. 21 and monolithic (single chip) magnetic sensors 150 shownin FIG. 22 are simultaneously produced.

[0141] As explained above, in the second embodiment, the strong magneticfield is provided at local space by utilizing the magnet array MB, andthe magnetic field thus provided is used to magnetize the the biasmagnet films of the GMR elements. The magnet array MB comprises the yokehaving through openings 202 serving as air gaps. Therefore, the magnetarray MB can provide a space close to the through openings 202 with amagnetic field whose magnitude is great and which is stably constant.Accordingly, even if the magnetic material having a high coersive forceis adopted to the bias magnetic film, the bias magnetic film can beassuredly magnetized. As a result, a high reliable magnetic sensor 110and 150 can be provided in which the direction of magnetization in thefree layer is stably returned to the initial-state direction even afterthe strong disturbance (e.g., a magnetic field whose magnitude isrelatively large) is added to the magnetic sensor.

[0142] In addition, the yoke 200 has the openings 203 formed at regionswhere the magnetic fields are unstable because of crossing (orcollision) of magnetic flux lines stemming from the poles. As a result,since the direction of the magnetic flux lines become stable, themagnetic field in the region in the neighborhood of the through opening202 becomes more stable. Further, the openings 203 are used to adjustthe distance between the substrate for the array 210 of the magnet arrayMB and the yoke 200 (i.e., the height of the yoke 200). Therefore, sinceit is possible to adjust the height of the yoke easily and desirably, anoptimum magnetic field can be provided for a region where the biasmagnetic film of the GMR element is disposed to be magnetized.

[0143] Moreover, the through hole 201 of the yoke 200 of the magnetarray MB has the shape which is not a square shape but which includesthe margin portions 201 b swelling outwardly from the square at each ofcorners of the square. Therefore, when forming the through hole 201 byetching, even if the corner of the through hole is not completely etchedas designed, the permanent bar magnet 230 can be assuredly inserted intothe through hole 201. It should be noted that this type of marginportion may preferably be formed at corners of the concavities 210 b.

[0144] The present invention is not limited to the above-mentionedembodiment, but various modifications can be applied within the scope ofthe present invention. For example, as shown in FIG. 20 representing afirst X-axis GMR element 301 taking as a representative example, narrowzonal portions 301 a may be separated at the upper portion of the biasmagnet films 301 b . . . 301 b disposed below both ends thereof.Further, an initializing coil 302 may be a double spiral type coilwherein a spiral coil 302-1 having a center point P1 and a spiral coil302-2 having a center point P2 are connected to each other. In thiscase, the first X-axis GMR element 301 is arranged between the centerpoint P1 and the center point P2, resulting in that currents parallel toeach other flow in the same direction (in a direction perpendicular tothe longitudinal direction of the narrow zonal portions 301 a) througheach conductor section of the initializing coil 302 passing below thefirst X-axis GMR element 301, thereby generating the initializingmagnetic field. Moreover, the initializing coil may be a multi-layeredcoil or may be a toroidal coil. Further, a testing coil that generates atesting magnetic field, in the direction perpendicular to theinitializing magnetic field generated by the initializing coil, forchecking a function of each GMR element may also be disposed in theinsulating layer above or below (Z-axis direction) the initializingcoil.

What is claimed is:
 1. A magnetic sensor comprising a magnetoresistiveeffect element including a pinned layer and a free layer comprising: abias magnet film composed of a permanent magnet for producing a biasmagnetic field in the free layer in a predetermined direction; and aninitializing coil that is provided in the vicinity of the free layer andapplies to the free layer a magnetic field in the direction same as thedirection of the bias magnetic field by being energized under apredetermined condition.
 2. A production process of a magnetic sensorcomprising, on a substrate, a pinned layer, a free layer and a biasmagnet film being a permanent magnet that applies a bias magnetic fieldto the free layer to form a magnetoresistive effect element having aresistance value varying according to a relative angle made by adirection of magnetization in the pinned layer and a direction ofmagnetization in the free layer, comprising: a step of preparing amagnet array configured such that plural permanent magnets are arrangedon a lattice point of a tetragonal lattice and a polarity of a magnetpole of each permanent magnet is different from a polarity of the otheradjacent magnet pole spaced by the shortest route; a step ofmanufacturing a wafer, including the substrates, on which pluralisland-like element films are interspersed, each element film includinga film that becomes the pinned layer, a film that becomes the free layerand a film that becomes the bias magnet film; and a step of disposingthe wafer in the vicinity of the magnet array so as to establish apredetermined relative positional relationship between the wafer and themagnet array, whereby the film that becomes the bias magnet film of theplural element films is magnetized by utilizing a magnetic field formedbetween one magnet pole of the magnet poles of the magnet array andother magnet pole, of the magnet poles of the magnet array, that isadjacent to the one magnet pole spaced by the shortest route.
 3. Aproduction process of the magnetic sensor claimed in Claim 2, whereinthe step of manufacturing the wafer includes a step of forming eachfilm, that becomes the free layer, of the plural element films in such amanner as to have a shape with a long axis and a short axis, and in sucha manner that at least one of the long axes of the films that become thefree layers of the plural element films is perpendicular to the longaxis of the other film, that becomes the free layer, of the pluralelement films and a step of forming the film that becomes the biasmagnet film at both ends of each film that becomes the free layer, inthe direction of the long axis, and wherein the predetermined relativepositional relationship in the step of magnetizing the film that becomesthe bias magnet film is a relative positional relationship, between thewafer and the magnet array, that matches the direction of magnetizationof the film that becomes the bias magnet film with the direction of thelong axis of the film that becomes the free layer having the bias magnetfilm provided at both ends thereof, by a magnetic field formed by themagnet array.
 4. A production process of the magnet sensor claimed inClaim 3, further comprising a step of arranging the wafer in thevicinity of the magnet array so as to establish a relative positionalrelationship, between the wafer and the magnet array, that is differentfrom the predetermined relative positional relationship, whereby thedirection of magnetization of the film, that becomes the pinned layer,of the plural element films is pinned by utilizing the magnetic fieldformed by the magnet array.
 5. A magnet array including plural permanentmagnets, each having an approximately rectangular parallelepiped shapeand having a sectional shape, perpendicular to one central axis of therectangular parallelepiped, which is approximately square, and eachhaving poles formed at both edge faces, one of which has theapproximately square shape perpendicular to the central axis of therectangular parallelepiped; wherein the plural permanent magnets arearranged in such a manner that each center of gravity of the edge faceshaving the approximately square shape is matched with a lattice point ofa tetragonal lattice, a certain side of sides forming one of the edgefaces of the plural permanent magnets disposed in a certain row of thetetragonal lattice and a certain side of sides forming one of the edgefaces of the other plural permanent magnets disposed in the same row ofthe tetragonal lattice is in a same straight line, all the edge faceshaving the square shapes of the permanent magnets are placed in anapproximately same single plane, and any two of the polarities of themagnetic poles of the permanent magnets disposed adjacent each other andspaced by the shortest route are different each other.
 6. A magnet arrayincluding plural permanent magnets, each having an approximatelyrectangular parallelepiped shape and having a sectional shape,perpendicular to one central axis of the rectangular parallelepiped,which is approximately square, and each having poles formed at both edgefaces, one of which has the approximately square shape perpendicular tothe central axis of the rectangular parallelepiped and a thin plate-likeyoke formed of a magnetic material; wherein the plural permanent magnetsare arranged in such a manner that each center of gravity of the edgefaces having the approximately square shape is matched with a latticepoint of a tetragonal lattice, a certain side of sides forming one ofthe edge faces of the plural permanent magnets disposed in a certain rowof the tetragonal lattice and a certain side of sides forming one of theedge faces of the other plural permanent magnets disposed in the samerow of the tetragonal lattice is in a same straight line, all the edgefaces having the square shapes of the permanent magnets are placed in anapproximately same single plane, and any two of the polarities of themagnetic poles of the permanent magnets disposed adjacent each other andspaced by the shortest route are different each other; and the yokecomprises plural through holes each of which has a shape which is theapproximately same as the sectional shape which is approximately squareand the holes being arranged at the positions where the permanentmagnets are disposed, and the yoke being arranged in such a manner thatthe same single plane in which all the edge faces of the permanentmagnets are placed is disposed between an upper surface and a lowersurface of the yoke when the permanent magnets are inserted into thethrough holes.
 7. A magnet array claimed in Claim 6; wherein the yokehas through openings serving as air gaps formed between the throughholes that are adjacent each other and that are spaced by a shortestroute.
 8. A magnet array claimed in Claim 7; wherein the yoke hasopenings at regions each of which is surrounding a center of gravity ofa square drawn by lines connecting the lattice points of the tetragonallattice in a plan view.
 9. A magnet array claimed in any one of claims 6to 8; wherein each of the through holes of the yoke has a square portionhaving a square shape which is the approximately same as the shape ofthe sectional square shape of the permanent magnet in a plan view and amargin portions swelling outwardly from the square at each of corners ofthe square portion.